1. Field of the Invention
The present invention relates to a portable type wireless communication apparatus and a wireless communication method.
2. Description of the Related Art
In recent years, with portable terminals or information apparatuses represented by so-called electronic notebooks, and notebook type personal computers, information is exchanged between apparatuses in such a manner that the information is obtained from a different apparatus or the information is transmitted to a different apparatus. In portable terminals, data such as sounds and images are converted into digital signals for communication.
Japanese Unexamined Patent Publication JP-A 5-241997 discloses one of the data communication methods adopted between apparatuses. With automatic data receivers shown as a prior art, a minimum amount of electric power which allows a data receipt part thereof to receive the data for reducing the consumed electric power at the time of waiting for communication, and the received data are stored in a buffer without operating a central processing unit (CPU) installed inside when the receipt of the data is detected.
It is necessary to suppress the consumed electric power of portable terminals because such terminals are generally driven by a small-size and light-weight battery device so that such terminals are portable. However, automatic data receivers are far from being sufficient in terms of a low consumption of the electric power because the electric power is constantly supplied to the data receipt part thereof. Consequently portable terminals use a communication apparatus which performs an intermittently receiving operation in communication, thereby suspending the operation of circuits except for the required time with the result that the consumed electric power is suppressed.
In communication between two or more wireless communication apparatuses of the prior art which carry out an intermittently receiving operation, a wireless communication apparatus is assumed which serves as a base station for controlling intensively a timing of outputting signals between the communication apparatuses. Moving stations which are none other than wireless communication apparatuses which do not serve as base stations are synchronized on the basis of a signal transmitted from the wireless communication apparatus serving as the base station, and a time when information can be received is determined using a timer incorporated in the moving stations. In moving stations, receipt circuits are operated only during the data receivable period so that the data receipt process is carried out every time each moving station detects the data that should be received. Except for the data receivable period, the operations of the receipt circuits are suspended in an attempt to reduce the consumed electric power.
Methods for communicating the data intermittently by setting a base station include base-station-controlled methods by which the data are communicated on the basis of signals transmitted from the base station and moving-station-controlled methods by which the data are communicated on the basis of signals transmitted from the moving stations.
Japanese Unexamined Patent Publication JP-A 5-252093 (1993) discloses one of the base-station-controlled communication methods. In the prior art described above, a timer provided on the moving station is operated with a synchronous signal transmitted from the base station which is set in a state of being capable of communicating with all the stations. When each of the moving stations cannot receive the synchronous signal, the receipt circuit is operated until the synchronous signal is detected. Upon the receipt of the synchronous signal, each of the moving stations renews the timer on the basis of the synchronous signal. Consequently, the communication is controlled under the guidance of the base station.
Each of the following patent publications discloses a technique for wireless data communication between moving stations and base station which can communicate with all the stations in the same manner as the prior art described above. Japanese Unexamined Patent Publication JP-A 5-207020 discloses a technique in which after the base station is determined, the moving stations synchronize frames with a signal transmitted from the base station to receive the data under a guidance of the base station. In time division multiplexing communication, each of the moving stations is set in the sleep state during a time except for slots used for the communication.
Furthermore, Japanese Unexamined Patent Publication JP-A 5-327586 discloses a technique in which an intermittent receipt period is prolonged and the receipt frequency is reduced because it is assumed that the frequency of detecting signals will increase in the case where intermittently receiving stations which are none other than the moving stations and detect the quality of channels judge that the channels are sufficiently high in quality. In the same technique, the intermittent receipt period is shortened when the channels are not favorable in quality.
Furthermore, Japanese Unexamined Patent Publication JP-A 5-75523 discloses a technique in which the moving stations synchronize frames with a signal transmitted from the base station to carry out a receipt process under the control of the base station. A concept of a super-frame is introduced so that a plurality of frames comprising time slots of a plurality of moving stations are integrated so that each of the moving stations are suspended during a time except for the slots used for communication at its own station. Still furthermore, Japanese Unexamined Patent Publication JP-A 5-183487 discloses a technique in which the receipt period is shortened when a call receipt process or a call receipt failure is generated. Consequently, the period for receiving the data intermittently is dynamically changed in accordance with the amount of communication.
Japanese Unexamined Patent Publication JP-A 62-26940 discloses one example of the moving-station-controlled communication method. In the communication method disclosed in JP-A 62-26940, when the receipt operation is initiated at power-on or by the registration of an identification number, a signal which requests the base stations which are in a state of being capable of communicating with all the stations, to establish synchronization with other stations is sent. On the other hand, along with transmission of the signal, the receipt period setting timer incorporated in the moving stations is reset. The moving stations are set in a state of being capable of receiving information on the basis of the timer for setting the receipt period. On the basis of a signal requesting the establishment of synchronization from the moving stations, the base station resets the receipt period control timer which corresponds to the moving station. The base station transmits the data to the moving stations in accordance with the receipt period control timer.
In the prior art in which the data are communicated intermittently by setting the base station described above, all the stations which attempt to establish communication adopt an intensive control in which such stations are synchronized with the base station via a signal transmitted from the base station. Consequently, one or more base stations must exist in the constituent devices of the communication system which comprises the base station and moving stations. When the communication system does not include a dedicated base station and comprises only moving stations, any of the moving stations must be set as a base station.
When it is determined that an operator determines which of the moving stations serve as the base station, the convenience of communication apparatuses will be unfavorable. Consequently, it is required to negotiate between respective communication apparatuses to determine which of the moving stations serves as the base station. When the negotiating function described above is incorporated in communication apparatuses, the structure will be complicated and the manufacturing cost thereof will rise. In addition, a transmission and reception process for carrying out the negotiation will be required so that the consumed electric power will rise.
FIG. 22 is a view showing a relation between respective communication apparatuses in the case where the data are communicated intermittently by setting the base station. FIG. 23 is a view showing a receipt pattern at each of the communication apparatuses. In FIG. 22, stations Z1, Z2, Z3 and Z4 which are communication apparatuses exist and stations Z1 and Z2, stations Z2 and Z3, and stations Z3 and Z4 are set in a position so that each of the pair of stations can communicate with each other. In addition, pairs of stations, for example, stations Z1 and Z3 except for the pairs described above are set in a position of being incapable of communicating with each other. In the prior art in which the base station is determined, stations which are capable of communicating with the base station do not serve as a base station. When each of the communication apparatuses is set in a relation shown in FIG. 22, any of the pairs of stations Z1 and Z3, stations Z2 and Z4, stations Z1 and Z4 is set as a base station.
For example, when a station Z1 and a station Z3 are set as the base stations, a station Z4 will be capable of communicating with the station Z3. In addition, although the station Z2 is capable of communicating with the station Z1 and the station Z3, a receipt pattern is set so that the station Z2 is capable of communicating with either of the two stations Z1 or Z3. When it is determined that the station Z2 is capable of communicating with the station Z1, the station Z2 synchronizes with the station Z1 which is the base station so that the station Z2 is capable of communicating with the station Z1. However, the station Z2 does not synchronize with the station Z3 so that the station Z2 is incapable of communicating with the station Z3. When the receipt patterns of the two stations do not agree with each other, the data receivable period of the two stations will be deviated from each other so that no communication is established even when the two stations are positioned at a place where the communication is possible.